U.S. patent number 4,451,867 [Application Number 06/415,542] was granted by the patent office on 1984-05-29 for electrically actuable ignition assembly.
This patent grant is currently assigned to Imperial Chemical Industries PLC. Invention is credited to James Robertson.
United States Patent |
4,451,867 |
Robertson |
May 29, 1984 |
Electrically actuable ignition assembly
Abstract
An electrically actuable ignition assembly comprising an
electric ignition element having insulated electrical leading wires
connected by means of conducting metal contact elements to the ends
of a secondary winding of insulated wire on a transformer ring
core. The transformer core and contacts are preferably encased in a
synthetic plastics case. The assembly is for use in blasting
operations in which multi-shot rounds are fired from an a.c. supply
by electromagnetic coupling of the supply with the secondary
winding by means of a single primary wire threaded through the ring
cores of a plurality of assemblies. The use of the metal contact
elements eliminates the previously used soldered joints between the
ignition element leading wires and the transformer secondary
winding.
Inventors: |
Robertson; James (Irvine,
GB6) |
Assignee: |
Imperial Chemical Industries
PLC (London, GB2)
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Family
ID: |
10524793 |
Appl.
No.: |
06/415,542 |
Filed: |
September 7, 1982 |
Foreign Application Priority Data
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Sep 28, 1981 [GB] |
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8129283 |
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Current U.S.
Class: |
361/248;
439/443 |
Current CPC
Class: |
F42D
1/05 (20130101); F41A 19/63 (20130101) |
Current International
Class: |
F42D
1/05 (20060101); F42D 1/00 (20060101); F41A
19/63 (20060101); F41A 19/00 (20060101); F42C
011/00 (); H01R 009/08 () |
Field of
Search: |
;339/98
;361/263,264,247,248 ;219/260,267 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0020241 |
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Dec 1980 |
|
EP |
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0020031 |
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Dec 1980 |
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EP |
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1520036 |
|
Aug 1978 |
|
GB |
|
1543705 |
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Apr 1979 |
|
GB |
|
2014380A |
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Aug 1979 |
|
GB |
|
2015832A |
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Sep 1979 |
|
GB |
|
2022222A |
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Dec 1979 |
|
GB |
|
1558582 |
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Jan 1980 |
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GB |
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2037494A |
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Jul 1980 |
|
GB |
|
2050079A |
|
Dec 1980 |
|
GB |
|
2091955A |
|
Aug 1982 |
|
GB |
|
Primary Examiner: Griffin; Donald A.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
I claim:
1. An electrically actuable ignition assembly comprising an encased
resistive electric ignition element having two terminals and a
length of electrical leading wire connected to each terminal, said
wire lengths extending outside the case, the portions of wire
outside the case being fully insulated, a transformer ring core
having an insulated length of electrical conductor wire wound
thereon as a secondary winding, and two electrically conducting
metal contact elements each electrically connecting an end-portion
of the secondary winding to a corresponding one of said lengths of
electrical leading wire to complete an electrical circuit across
said terminals, said contact elements having portions penetrating
the insulating layer on the respective wires and contacting the
wire.
2. An assembly as claimed in claim 1 wherein the contact elements
are portions of thin metal sheet, each portion being formed with
one or more slots extending from at least one edge thereof, said
slots being of such width that when the insulated wire portion is
inserted into the slot the metal edges and the slot sides penetrate
the insulating material on the wire and make electrical contact
with the wire.
3. An assembly as claimed in claim 2 wherein the metal contact
elements are each provided with at least two slots.
4. An assembly as claimed in claim 3 wherein the said slots are
disposed to extend from opposite edges of the element.
5. An assembly as claimed in any one of claims 2 to 4 inclusive
wherein each contact element comprises a portion of metal sheet
doubled to provide two substantially parallel portions with a
portion connecting the parallel portions, slots being formed in the
opposing free edges of the parallel portions.
6. An assembly as claimed in claim 1 wherein the transformer ring
core is a toroidal ring core of ferrite material.
7. An assembly as claimed in claim 6 wherein the toroidal ring core
with its secondary winding, the contact elements and the portions
of wire adjacent thereto are encased in a synthetic plastics case,
the case being provided with apertures coincident with the central
opening of the toroidal ring core through which apertures a loop of
insulated wire may be threaded to serve as a primary winding for
the transformer.
8. An assembly as claimed in claim 7 wherein the apertures are
formed so as to leave a portion of the inside circumferential
surface of the ring core exposed.
9. An assembly as claimed in claim 1 wherein the case is
constructed in two portions, one portion being a lower or base
portion and the other an upper or lid portion, one portion of the
case being adapted to accommodate the end portions of the
electrical leading wires of the ignition element and the other
portion being adapted to accommodate the transformer ring core, the
secondary winding and the contact elements, the case portions being
adapted to close together so as to bring each contact element into
contact with an electrical leading wire and an end portion of the
secondary winding.
10. An assembly as claimed in claim 9 wherein the case portions are
formed with at least one projection and at least one corresponding
recess whereby, on closing the case, the two case portions become
firmly locked together.
11. An assembly as claimed in claim 9 wherein the case is made as a
single injection moulding with the two parts being joined by a thin
hinge portion.
Description
This invention relates to an electrically actuable ignition
assembly adapted for electromagnetic coupling to an a.c. source of
firing energy. More particularly the invention relates to an
assembly comprising an encased resistive electric ignition element
having insulated electrical leading wires external to said casing
electromagnetically coupled to a transformer ring core by at least
one loop of insulated wire wrapped as a secondary winding on the
transformer core.
Electromagnetically coupled detonator assemblies wherein an
electric detonator is electromagnetically coupled to a ferrite ring
are described in our United Kingdom Patent Specification No. 2 022
222A and are commercially available under the trade name
`Magnadet`. In these detonators a continuous circuit of conductor
wire is connected across the terminals of the encased resistive
electric ignition element of a detonator, a portion of leading wire
external to the casing being fully insulated and wound as a
secondary winding of 3-5 turns on a toroidal ferrite core. For ease
of manufacture the toroidal core and secondary winding are
assembled in a first operation and the detonator is separately
assembled with a length of insulated external leading wire
extending from each of the two terminals of the resistive elements
to a position outside the casing. A bared end portion of each
leading wire is electrically connected respectively to bared
portions of the two ends of the secondary winding to complete the
electrical circuit across the ignition element. The joints between
the wires and the toroidal ferrite core are encased in a synthetic
plastics protective casing thereby fully insulating the external
electrical circuit of the detonator. The protective casing is
provided with a central opening through which an electric conductor
wire may be threaded as a single loop primary winding for the
toroidal transformer core and connected to a suitable source of
alternating current for firing the detonator. A single primary wire
may be threaded through several toroidal rings for the simultaneous
initiation of all the associated detonators. These
electromagnetically coupled detonators have attractive safety
characteristics, being substantially immune to stray electric
currents and static electricity and being frequency selective so
that signals outside a designed band of about 10 to 100 kHz are
effectively attenuated. The detonators are also attractive to users
as the connection of multi-shot rounds to the firing source for
blasting is easily and rapidly made, the wiring joints in the
detonator circuit being substantially eliminated. In the `Magnadet`
detonators currently used the joints between the secondary winding
and the external leading wires from the detonator element are made
by twisting and/or soldering end portions of the wires from which
the insulating material, usually polyvinyl chloride, has been
stripped. The making of these joints therefore requires several
time-consuming operations. It is an object of this invention to
provide a transformer coupled electrically actuable ignition
assembly which does not necessitate the formation of joints between
prestripped wire ends.
In accordance with this invention an electrically actuable ignition
assembly comprises an encased resistive electric ignition element
having a length of electrical leading wire connected to each of its
two terminals and extending outside the case, the portions of wire
outside the case being fully insulated, a transformer ring core
having an insulated length of electrical conductor wire wound
thereon as a secondary winding, and two electrically conducting
metal contact elements each electrically connecting an end portion
of the secondary winding to a corresponding one of said lengths of
electrical leading wire to complete an electrical circuit across
said terminals, said contact element having portions penetrating
the insulating layer on the respective wires.
The contact elements are preferably portions of thin metal sheet,
each portion being formed with one or more slots extending from at
least one edge thereof, said slots being of such width that when
the insulated wire portion is inserted into the slot the metal
edges at the slot sides penetrate the insulating material on the
wire and make electrical contact with the wire. Preferably the
metal contact elements are each provided with at least two slots
and conveniently the slots are disposed to extend from opposite
edges of the element. If desired, the contact element may comprise
a portion of metal sheet doubled to provide two substantially
parallel portions with a portion connecting the parallel portions,
slots being formed in the opposing free edges of the parallel
portions.
The transformer ring core is preferably a toroidal ring core of
ferrite material. For protection in use the toroidal ring core with
its secondary winding, the contact elements and the portions of
wire adjacent thereto are preferably encased in a synthetic
plastics case, the case being provided with apertures coincident
with the central opening of the toroidal ring core through which
apertures a loop of insulated wire may be threaded to serve as a
primary winding for the transformer. The apertures should
preferably be such as to leave a portion of the inside
circumferential surface of the ring core exposed. The preferred
case provides an annular chamber to accommodate the toroidal ring
and a communicating conduit adapted to accommodate and firmly
retain the contact elements and wire portions. The toroidal ring
core is preferably supported on internal projections in the annular
chamber such that an annular air space is provided around the
outside of the ring core to provide protection against impact.
The case is preferably a substantially rigid case, fabricated for
example from polypropylene.
Conveniently the case is constructed in two portions, one portion
being a lower or base portion and the other an upper or lid
portion. One portion may be adapted to accommodate the end portions
of the electrical leading wires of the ignition element and the
other portion adapted to accommodate the transformer ring core, the
secondary winding and the contact elements, the case portions being
adapted to close together so as to bring each contact element into
contact with an electrical leading wire and an end portion of the
secondary winding. Preferably the case portions are of
substantially equal size, the plane of contact between the portions
being the medial plane of the case. The case portions are
preferably formed with at least one projection and at least one
corresponding recess whereby, on closing the case, the two case
portions become firmly locked together, for example, by snap-lock
engagement. In an especially preferred assembly the case is made as
a single injection moulding with the two parts being joined by a
thin hinge portion. For this form of case polypropylene is the
preferred construction material because of its superior flexing
properties .
The invention is further illustrated by the preferred embodiment
which is hereinafter particularly described, by way of example,
with reference to the accompanying drawings wherein
FIG. 1 shows diagramatically in perspective the separate parts of
an assembly of the invention,
FIG. 2 shows in perspective the assembly with the parts of FIG. 1
positioned in the open case of the assembly,
FIG. 3 shows in perspective the assembly of FIGS. 1 and 2 with the
case closed, part of the case being cut away,
FIG. 4 is a cross-section on the line IV--IV of FIG. 3,
FIG. 5 is a cross-section on the line V--V of FIG. 3.
Referring to FIG. 1, the assembly comprises a case 10, toroidal
ferrite ring core 11, secondary winding 12, contact elements 13 and
14 and electric detonator 15 having two electric leading wires 16
and 17. The case 10 is injection moulded as a single moulding
having two portions conveniently designated as lower portion 18 and
upper portion 19, joined by a thin hinge portion 20. Both portions
18 and 19 consist of generally hollow open topped boxes 21 and 22,
and generally solid lateral portions 23 and 24 extending
respectively from a side of each hollow portion 21 and 22.
The boxes 21 and 22 have D-shaped central apertures 25 and 26
disposed centrally one in each of the bottom faces 27 and 28 of the
boxes 21 and 22. Vertical rectangular upstands 29 and 30 project
from the faces 27 and 28 at the side of the apertures 25 and 26
nearest to the lateral portions 23 and 24, the upstands being
transverse to the lateral portions 23 and 24. The boxes 21 and 22
also each have three internal webs 31, each shaped with a
supporting shoulder 32 so as to support the ring core 11 with an
annular space between the ring core and the box sides.
The solid portions 23 and 24 are formed with shallow grooves of
semicircular cross-section 33,34,35,36, and deep grooves 37,38,39
and 40, the shallow grooves being approximately of the same radius
as the leading wires 16 and 17 and the deep grooves being of a
depth greater than the diameters of the leading wires 16 and 17 and
the secondary winding 12. The grooves 37,38,39 and 40 are formed
with pockets 41,42,43 and 44, one in each groove, adapted to
receive an end of a contact element 13 and 14. The solid portion 23
is formed with a projecting portion 45, consisting of a transverse
rib 61 and locking hooks 47 and 48, adapted to enter and engage in
a recess 46 formed in the solid portion 24, the locking hooks 47
and 48 being adapted to lock with corresponding steps 57 and 58 in
the outer side walls of apertures 59 and 60 formed in the base of
the recess 46, as shown in FIG. 5.
The contact elements 13 and 14 are flat elongated metal stampings
formed with elongated slots 49,50,51 and 52 extending from the ends
of the elements, the slots being generally parallel sided and
approximately the width of the metal core of the insulated wire of
the leading wires 16 and 17 and the end portions 55 and 56 of the
secondary winding 12 which they are designed to contact. At the end
of the slots the slot sides are divergent to assist entry of the
insulated wires. The elements 13 and 14 are formed with tapered
projecting shoulder portions 53 at their lower ends to act as
locking barbs when the elements are inserted into pockets 43 and 44
respectively.
The ring core 11 is in the form of a short hollow cylinder
(although it is conventionally termed a toroid) and the second
winding 12 consists of 3 turns of plastics insulated wire of the
same kind as used for the detonator leading wires 16 and 17.
In putting the assembly together the parts are first assembled as
shown in FIG. 2. The ring core 11 is placed in the box 22 around
the upstand 30 with its outer edge resting on the shoulders 32 so
as to leave an annular space 54 around the core 11. The core 11 is
oriented so that the secondary winding 12 lies between the upstand
30 and the lateral portion 24 and the end portions 55 and 56 of the
secondary winding 12 are placed respectively in the grooves 39 and
40. The lower ends of the contact elements 13 and 14 are then
inserted into pockets 43 and 44 respectively, the wire portions 55
and 56 entering the slots 49 and 52 respectively. The sides of the
slots 49 and 52 cut through the plastics insulation and make
electrical contact with the metal wire cores 62 and 63 of the wire
portions 55 and 56 and the shoulders 53 of the elements 13 and 14
become locked in the pockets 43 and 44 as shown in FIG. 4. The end
portions of the leading wires 16 and 17 are trained over the
transverse rib 61, the wire 16 being inserted in the grooves 33 and
37 and wire 17 being inserted in grooves 34 and 38, the wire ends
extending through the pockets 41 and 42.
The assembly is completed by folding the upper portion 18 around
the hinge 20 to close the two portions 18 and 19 together as shown
in FIG. 3 with the projecting portion 45 locked into the recess 46
(see FIG. 5). In this closing operation the upper ends of the
contact elements 13 and 14 are forced into pockets 41 and 42
respectively so that the wires 16 and 17 enter the slots 50 and 51
respectively, the sides of the slots cutting the wire insulation
and making electrical contact with the metal wire core as shown in
FIG. 4. Thus electrical contact is established between secondary
winding portion 55 and detonator leading wire 16 and between
secondary winding portion 56 and detonator leading wire 17 to
provide a continuous circuit coupling the secondary winding 12 and
the ignition element of detonator 15. In the closed position the
top edges of the boxes 21 and 22 abut each other. The upstand 29
abuts upstand 30 to provide an annular chamber enclosing the ring
core 11 with an air space around almost all the ring core surface.
A portion of the inner curved surface of the ring core 11
coincident with the curved rims of the D-shaped apertures 25 and 26
is left uncovered. The leading wires 16 and 17 are bent over the
rib 61 and firmly gripped between rib 61 and the base and side
walls of the recess 46 so that the joints between the wires and the
contact elements are protected from tensioning of the wires in use.
In the closed case the grooves 33,34,35 and 36 form tubular
passages closely fitting around the wires 16 and 17 through which
passages the wires 16 and 17 emerge.
It is generally convenient to connect the detonator 15 as the last
item of the assembly. Thus, if desired, the assembly of FIG. 2
except for the detonator may be prepared at one site and at another
site the detonator may be added and the assembly closed to complete
the assembly as shown in FIG. 3.
In use, the detonator 15 is fired by threading an insulated
electrical conductor wire through the apertures 25 and 26 and the
ring core 11 and passing an alternating current of appropriate
frequency through the conductor wire, whereby a firing current is
electromagnetically induced in the secondary winding 12 and in the
ignition element of the detonator. If desired, a single conductor
wire may be threaded through the ring cores of several assemblies
to fire several detonators simultaneously from a single source of
electrical energy.
* * * * *